The coating of plastic substrates, in particular flexible plastic substrates, with relatively hard and brittle layer materials, such as, e.g., oxides or nitrides, is affected by the difficulty that the plastic substrate can buckle owing to mechanical stresses. This can have the effect that the applied layer is detached partially or even completely from the substrate. In order to reduce this problem, it is possible to firstly apply an adhesion-promoting layer to the plastic substrate before the application of further layers. However, this requires an additional method step.
A further possible way to improve the adhesion of layers on plastic substrates consists in mechanically roughening the plastic substrate before the layers are applied. This generally has a negative effect on the optical properties, however, with it being possible for the transmission to be adversely affected particularly in the case of optical elements made of plastic.